The Standard Model and Beyond

What is the last piece of the Standard Model we are searching for? What new physics lies beyond the Standard Model?

The Standard Model of particle physics is a theory of three of the four known fundamental interactions and the elementary particles that take part in these interactions. These particles make up all visible matter in the universe. Every high energy physics experiment carried out since the mid-20th century has eventually yielded findings consistent with the Standard Model. Still, the Standard Model falls short of being a complete theory of fundamental interactions because it does not include gravitation, dark matter, or dark energy.

The Higgs boson plays a unique role in the Standard Model, by explaining why the other elementary particles, the photon and gluon excepted, are massive. In particular, the Higgs boson would explain why the photon has no mass, while the W and Z bosons are very heavy. In fact, for a number of reasons the Standard Model could not exist as a standalone theory without the Higgs boson. At the same time, there are a number of theoretical difficulties with the SM Higgs boson which have led physicists to believe there may be some type of new physics about to be discovered that resolves these difficulties (Supersymmetry, extra hidden dimensions, technicolor etc...). As yet, no experiment has directly detected the existence of the Higgs boson.

The main questions at the frontiers of particle physics can be summarised as follows:

What generates the masses of the fundamental particles? Is it the Higgs boson or something else?

If the Higgs boson exists, what solves the theoretical difficulties? Is it Supersymmetry, extra hidden dimensions or something else?

What is dark matter and dark energy?

How is gravity incorporated into the Standard Model? Can all the particles and interactions be described by a single Grand Unified Theory?

For a more detailed description of the Standard Model, its development and possible new physics visit these links: